Extreme ultraviolet (EUV) - lithography at a wavelength around 13.5 nm is considered as the most promising successor of optical projection lithography. This paper reviews simulation models for EUV lithography. Resist model parameters are calibrated with experimental data. The models are applied for the investigation of the impact of mask multilayer defects on the lithographic process.

Rigorous simulation of light diffraction from optical and EUV masks predicts phase effects with an aberration like impact on the imaging performance of lithographic projection systems. This paper demonstrates the application of advanced modeling and optimization methods for the compensation of mask induced aberration effects. It is shown that proper adjustment of the wavefront results in significant reduction of best focus differences between different features.

Lithographic masks are an important and increasingly complex part of systems for advanced optical and extreme ultraviolet (EUV) lithography. They introduce polarization and phase effects with a significant impact on the entire system performance. Rigorous electromagnetic field (EMF) modeling of the mask is indispensable for a predictive simulation of lithographic processes. This paper describes several alternative mask models and their integration into a lithography simulation framework. Several examples demonstrate the relevance of an accurate mask diffraction modeling for the prediction of the lithographic process performance.

Different mask models have been compared: rigorous electromagnetic field (EMF) modeling, rigorous EMF modeling with decomposition techniques and the thin mask approach (Kirchhoff approach) to simulate optical diffraction from different mask patterns in projection systems for lithography. In addition, each rigorous model was tested for two different formulations for partially coherent imaging: The Hopkins assumption and rigorous simulation of mask diffraction orders for multiple illumination angles. The aim of this work is to closely approximate results of the rigorous EMF method by the thin mask model enhanced with pupil filtering techniques. The validity of this approach for different feature sizes, shapes and illumination conditions is investigated.

This paper uses advanced modeling techniques to explore interactions between the two lithography processes in a litho-cure-etch process and to qualify their impact on the final resist profiles and process performance. Specifically, wafer topography effects due to different optical properties of involved photoresist materials, linewidth variations in the second lithography step due to partial deprotection of imperfectly cured resist, and acid/quencher diffusion effects between resist materials are investigated. The paper highlights the results of the simulation work package of the European MD3 project.

This paper aims at identifying appropriate bottom anti-reflective coatings (BARCs) for double patterning techniques such as Litho-Freeze-Litho-Etch (LFLE). A short introduction into the employed optimization methodology, including variables, figures of merit, models and optimization algorithms is given. A study on the impact of a refractive index modulation caused by the first lithographic step is presented. Several optimization surveys taking the index modulation into account are set forth, and the results are discussed. In addition to optimization procedures aiming at optimizing one litho step at a time, a co-optimization study for both litho steps is proposed. Finally, two multi-objective optimization procedures that allow for a post-optimization exploration and selection of optimum solutions are presented. Numerous solutions are discussed in terms of their anti-reflectance behavior and their manufacturing feasibility.

This paper discusses the modeling of reversible contrast enhancement layers (RCEL) for advanced optical lithography. An efficient implementation of the Waveguide method is employed to investigate the process capability of RCEL and to identify the most appropriate material and exposure parameters. It is demonstrated that the consideration of near field diffraction effects and of bleaching dynamics is important to achieve correct results. A large refractive index of the resist and the RCEL improves the achievable lithographic performance. It is shown that RCEL layers can be used to enhance the performance of a NA=0.6 scanner to create a high contrast images with a pitch of 80nm.

This paper employs rigorous electromagnetic field (EMF) solvers to investigate the printing behavior of EUV multilayer defects. A compression model is applied to compute the defect induced deformation of the multilayer. A fully rigorous Waveguide method is used to simulate the light diffraction from the defective EUV mask. This fully rigorous method is compared with two other methods: A decomposition method combined with the Waveguide algorithm and a hybrid method which computes the multilayer with an analytical method based on the Fresnel-formulas and the mask absorber with a finite-difference time-domain (FDTD) algorithm. Cross sections and the critical dimensions (CD) of the printed wafer features are evaluated by the application of a threshold model to the computed aerial images. The printability of the multilayer defects and their impact on the CD of printed absorber features are investigated versus the defect position, size and other parameters of the defect model. Finally, the influence of the mask absorber properties on the defect-induced CD variation is investigated. It is shown that the printability of the defect depends on the absorber properties.

This paper employs the Waveguide decomposition method as an efficient rigorous electromagnetic field (EMF) solver to investigate three dimensional mask-induced imaging artifacts in EUV lithography. The major mask diffraction induced imaging artifacts are first identified by applying the Zernike analysis of the mask nearfield spectrum of 2D lines/spaces. Three dimensional mask features like 22nm semidense/dense contacts/posts, isolated elbows and line-ends are then investigated in terms of lithographic results. After that, the 3D mask-induced imaging artifacts such as feature orientation dependent best focus shift, process window asymmetries, and other aberration-like phenomena are explored for the studied mask features. The simulation results can help lithographers to understand the reasons of EUV-specific imaging artifacts and to devise illumination and feature dependent strategies for their compensation in the optical proximity correction (OPC) for EUV masks. At last, an efficient approach using the Zernike analysis together with the Waveguide decomposition technique is proposed to characterize the impact of mask properties for the future OPC process.

As the technology marches towards the 32nm node and beyond in semiconductor manufacturing, double patterning and double exposure techniques are currently regarded as the potential candidates to produce lines and spaces (L&S) and contact holes (C/H), respectively. In this paper, the Waveguide method, a rigorous electromagnetic field (EMF) solver, is employed to investigate the impact of wafer topographies on two specific double patterning techniques. At first, the topography effects induced by the first patterning on the second lithography process in a lithography-etch-lithographyetch (LELE) process are demonstrated. A new methodology of the bottom anti-reflective coating (BARC) optimization is proposed to reduce the impact of wafer topography on resist profiles. Additionally, an optical proximity correction (OPC) of the second lithography mask is demonstrated to compensate the wafer topography induced asymmetric deformations of line ends. Rigorous EMF simulations of lithographic exposures are also applied to investigate wafer topography effects in a freezing process. The difference between the optical properties of the frozen (first) resist and the second resist potentially causes linewidth variations. Quantitative criteria for tolerable refractive index and extinction differences between the two resist materials are given. The described studies can be used for the optimizations of topographic waferstacks, the OPC of the second litho mask, and for the development of resist materials with appropriate optical properties.

In this work, a framework for the assessment of different double exposure techniques is laid out. Both the simulation environment and the utilized models, derived from well-established resist models, are discussed. Numerous simulation results are evaluated to investigate strengths and weaknesses of different double exposure approaches. Non-linear superposition techniques are examined in respect of their process performance for both standard and sub 0.25 k1 values. In addition to a study of these effects in the scope of basic layouts, an application to interference-assisted lithography (IAL) is proposed and discussed.

This article reviews standard and advanced modeling techniques in lithography simulation. Rigorous electromagnetic field solvers such as the Waveguide Method and finite-difference time-domain (FDTD) algorithms in combination with vector imaging models predict the image formation inside the photoresist. Semi-empirical macroscopic and microscopic models describe physical and chemical phenomena during the processing of resists. Various local and global optimization techniques are applied to identify the best exposure and process parameters. Several examples demonstrate the application of predictive simulation for the exploration of future lithography options and for the optimization of existing technologies. This includes the consideration of mask material parameters in source/mask optimization, the evaluation and comparison of different options for double exposure and double patterning techniques, and the investigation of mask-induced imaging artifacts in EUV-lithography. Selected examples illustrate the application of lithography simulation for the modeling of cost efficient alternative exposure techniques for special applications of micro- and nanotechnology.

Double patterning is regarded as a potential candidate to achieve the 32nm node in semiconductor manufacturing. A key problem for a standard litho-etch–litho-etch (LELE) double patterning process is to evaluate and tackle the impact of the wafer topography resulting from the hardmask pattern on the second lithography step. In this paper, we apply rigorous electromagnetic field (EMF) solvers to investigate the wafer topography effects. At first, the studied 3D mask is split into two masks. The topography resulting from the exposure with the first split mask is described by a patterned hardmask. Based on that, the bottom antireflective coating (BARC) thickness of the second wafer stack is optimized. Alternatively, a two beam interference and the full diffraction spectrum of the second mask are used as the illumination of the wafer stacks, respectively. Finally, simulated 3D resist profiles for different BARC thicknesses are shown. The importance of wafer topography impact, the optimization of topographic wafer stacks, and the possible solutions to compensate for the impact of the wafer topography are discussed.

A new and optimized electromagnetic field (EMF) solver based on the waveguide method with a decomposition technique for rigorous optical and extreme ultraviolet (EUV) mask near field simulations is presented. The implemented software algorithm enables full three dimensional (full 3D) mask simulations as well as three dimensional mask simulations based on a parallelized decomposition technique (Q3D, "Q" stands for "quasi"). After a short introduction to the waveguide method and to an optimized mask description, the basis of the decomposition technique and its parallelization are presented. Subsequently the capabilities of the new electromagnetic field solver are demonstrated by simulations of advanced optical and EUV imaging problems. Simulations of larger sized mask areas and of standard sized defective EUV mask areas using the decomposition technique are shown. Finally, a further reduction of computation time using parallelization is demonstrated.

A new and optimized waveguide based electromagnetic field solver with decomposition technique for rigorous optical and extreme ultraviolet (EUV) mask near field simulations is presented. The model allows to perform full three dimensional (full 313) simulations as well as three dimensional simulations based on a decomposition technique (Q3D, "Q" means "quasi"). After a short introduction of the waveguide method the decomposition technique is presented. Subsequently the capabilities of the new electromagnetic field solver are demonstrated exemplarily based on state-of-the-art optical and EUV systems. The simulation of larger mask areas and the fast simulation of standard sized mask areas is shown. A comparison between the full 3D and the Q3D approach demonstrates the field of application of the decomposition technique.